In total, 1221 studies were retrieved as potentially relevant literature reports through the initial searches in different databases and after removing the duplicates, 1013 were left. Majority of potentially irrelevant literatures were excluded after reviewing the browsing title or abstract. After retrieving 30 full-length manuscripts, finally, 12 articles [7-9,18,19,25-31] of 19 studies were eligible for data extraction and meta-analysis. The flow chart of the studies enrolled in the current study can be found in Figure 1.
19 studies (12 articles) met the inclusion criteria and a total of 21301 participants were included in the study. Four articles [8, 16, 24, 29] were divided into two or four studies as the participants were categorized into several groups according their characteristics. Eight studies [7-9,19,28-30] addressed the association between sarcopenia and hypertension, and 11 studies [18,25-27,31] focused on the association between handgrip strength and hypertension. The sarcopenia was defined by three methods, the European Working Group on Sarcopenia in Older People (EWGSOP) criteria , the Asian Working Group for Sarcopenia (AWGS) criteria, and ASM/weight (kg) less than one standard deviation (SD). The hypertension was defined as systolic blood pressure (SBP) >140 mmHg or diastolic blood pressure (DBP)>90 mmHg. Handgrip strength was diagnosed by dynamometers according to the protocol from the Institute of Medicine . The included studies were published between 2013 and 2019 and the sample size ranged from 72 to 4771. The participants’ demographic characteristics in the included studies can be found in Supplementary Table 1 and Supplementary Table 2.
Six studies were conducted in China [18,19,28,31], two each in Republic of Korea  and Japan , and United States [9,25,34,35], one each in Turkey , Switzerland , Italy , and Spain . Most of the studies were cross-sectional studies except two cohort studies [7,9]. The characteristics of the included studies and patients were summarized in Table 1 and Table 2.
Quality assessment of studies
Newcastle-Ottawa Scales for the eligible studies were presented in Supplementary Table 3 and all included studies were found to exhibit an acceptable quality. Four studies were evaluated as 6 stars, 6 studies were 7 stars, and 2 studies were 8 stars.
The association between sarcopenia and hypertension
All the eight eligible studies have reported the ORs of hypertension, and the ORs ranged from 0.41 to 4.38. When pooled the ORs together, the summarized ORs was 1.29 (95% CI=1.00-1.67, P=0.04) with a moderate heterogeneity (I2 = 74%). The detailed information could be found in Figure 2 and Supplementary Figure 1.
To explore the sources of heterogeneity, the subgroup analysis was performed by categorizing the studies according to the ethnicity of the participants and the Newcastle-Ottawa Scales than were equal to or more than 7 stars. The Asian group included 4 studies from China and Korea, the Caucasian group included four studies conducted in United States, Italy, Spain, and Turkey. The summarized ORs for the Asian group 1.50 (95% CI = 1.35-1.67, P = 0.00) was significantly higher than that of Caucasian group 1.08 (95% CI=0.39-2.97, P=0.88). The heterogeneities for the two subgroups were significantly decreased to I2 = 34% and I2 =40%. When the studies with low quality were removed (Newcastle-Ottawa Scales<6), the overall OR were 1.53 (95%CI = 1.37-1.71, P = 0.00) with lower heterogeneity (I2 = 2.62%). More data is presented in Figure 3 and Figure 4.
The association between handgrip strength and hypertension
Eleven studies have provided the data on association between handgrip strength and hypertension, and among them ten studies have reported the odds ratios and 95% CI. The overall odds ratios and 95% CI was 0.99 (95% CI=0.80-1.23, P=0.93) with a higher heterogeneity (I2 = 76%) and significant publication bias (P < 0.01). The detailed data can be found in Figure 5.
As shown in Figure 6 and Figure 7, in order to explore the sources of heterogeneity and publication bias, the included studies were categorized into two groups by the gender of the participants. For the males, the pooled OR was 1.14 (95%CI=0.91-1.43, P=0.27) with an acceptable heterogeneity (I2 = 31%) and without publication bias (P > 0.05). The female group was not showing any statistically significant difference with an OR as 0.81 (95%CI=0.52-1.26, P=0.34, I2 = 45%) without publication bias (P > 0.05).
Seven studies have reported the β value and standard error of the linear regression on hypertension and the pooled β value was -1.57 with an SE equal to 1.03, and the heterogeneity was 99%. As two studies have provided the data on different body mass indexes, two more subgroup analysis were done, such as underweight or normal body mass index group (OR=1.04, 95%CI=0.81-1.33, P=0.77), and overweight or obese body mass index group (OR=1.18, 95%CI=0.94-1.41, P=0.16). The data was presented in Supplementary Figure 3 and Supplementary Figure 4.
Most of the analysis except one has shown potential publication bias among the included trials according to Begg rank correlation analysis and Egger weighted regression analysis (P value of the analysis was more than 0.05). The detailed potential publication bias of each analysis can be found in Supplementary Table 4